Crystal protein synthesis by a local isolate of Bacillus thuringiensis was monitored and compared in association with growth and sporulation in media differing in mineral element content. Mg and Cu were the most important metals for the biosynthesis of 135 kDa and 65 kDa toxin components in that the former was essential and the latter was greatly stimulatory at 10(-6) to 10(-7) M concentration. Also the inclusion of Mn favored toxin production at concentrations ranging from 3 x 10(-4) to 10(-5) M. The omission of Zn and Ca had no effect on toxin formation. Crystal protein synthesis and sporulation did not generally seem to be co-regulated by the minerals as these processes responded differently to mineral levels. There was no evidence for suppression of biosynthesis by inorganic phosphate over a range of 3 to 100 mM. Crystal protein production was more efficient in buffered medium, especially when the initial pH was adjusted to 6.5. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.